Method for sampling and determining the presence of contaminants in recyclable plastic materials

ABSTRACT

An inspection system for sampling and determining the presence of residues of contaminants within plastic materials to be recycled from used plastic materials such as plastic beverage bottles or plastic food containers includes a chemical sniffing apparatus, or alternatively an optical scanner, for detecting the contaminants as the plastic materials are rapidly moved along a conveyor past a series of stations. Recycled food or beverage bottles are fed through a shredder in-line with the conveyor and the shredded plastic material from the bottles is fed to a washer. The bottles and shredded material may be tested for contaminants at any location in an in-line process. In one exemplary system first the bottles are tested prior to entry into the shredder in order to remove bottles containing gross contaminants. Second the shredded material emerging from the shredder is immediately tested for contaminants at an elevated temperature caused by the shredding process and contaminated materials are separated or sorted out from the uncontaminated material. Third, the materials are again tested for contaminants as they emerge from the washer once again taking advantage of the elevated temperature of the materials which is conducive to the emission of vapors of the contaminants. Contaminated materials are again sorted from the uncontaminated supply of materials to be used for the fabrication of new plastic food or beverage bottles.

This application is a divisional of U.S. application Ser. No.08/251,373, filed on May 31, 1994, now U.S. Pat. No. 5,569,606, which isa continuation-in-part of prior U.S. application Ser. No. 07/890,863filed Jun. 1, 1992, now U.S. Pat. No. 5,352,611, and assigned to thesame assignee as the present invention described herein, the entirecontents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

The present invention relates to an inspection system for sampling anddetermining the presence of certain substances, such as residues ofcontaminants within plastic materials to be recycled from containerssuch as plastic polyethylene terephthalate (PET) beverage bottles orplastic food containers. More specifically, the present inventionrelates to an improved sampling and analyzing system and method fordetermining the presence of substances such as residues of contaminantsin plastic materials from recycled articles such as beverage bottles orother containers--e.g., as the material is rapidly moved along aconveyor past a series of test stations in a material washing andsorting system.

In many industries, including the beverage industry, products arepackaged in containers which are returned after use, washed andrefilled. Typically refillable containers, such as beverage bottles, aremade of glass which can be easily cleaned. These containers are washedand then inspected for the presence of foreign matter.

Glass containers have the disadvantage of being fragile and, in largervolumes, of being relatively heavy. Accordingly, it is highly desirableto use plastic containers because they are less fragile and lighter thanglass containers of the same volume. However, plastic materials canabsorb a variety of compounds which may later be desorbed into theproduct thereby potentially adversely affecting the quality of theproduct packed in the container. Examples of such compounds include butare not limited to ammonia, organic nitrogenous compounds, andhydrocarbons including gasoline and various cleaning fluids includingsoaps and detergents.

However, if these plastic containers, or the materials from which eachis made can be reliably inspected for contaminants of very highsensitivity, contaminated plastic bottles or materials can be separatedfrom uncontaminated containers or materials, and the good containers ormaterials can be recycled.

The aforementioned U.S. application Ser. No. 07/890,863, now U.S. Pat.No. 5,352,611, describes inspection techniques for determining thepresence of contaminants in used, plastic beverage containers, or inshredded or flaked plastic material from which the containers were made.

The present invention is directed to improvements to the techniquesdescribed in the prior application Ser. No. 07/890,863, now U.S. Pat.No. 5,352,611, regarding recycling of plastic materials, includingmaterials from which such used plastic beverage containers were made.

In order to recycle plastic materials such as from PET beverage bottlesfor use in the fabrication of new bottles, it is necessary to ensurethat the recycled material does not contain any potentially harmfulcontaminants of the types described hereinbefore.

While various efforts have been made for removing unwanted contaminatedplastics from an incoming stream of beverage bottles, and then shreddingthe bottles and thoroughly washing the shredded plastic material so asto remove potentially harmful contaminants from the shredded or flakedmaterial, a need in the art exists for improved inspection of recycledplastic materials. In particular, it would be advantageous to haveon-line, real-time, chemical monitoring of recycled plastic materialssuch as bottles or resulting flake at any stage of processing,particularly at any stage of pre-processing, including sortation,cleaning, washing, flaking, pelletizing and preform and/or bottlemanufacturing to ensure that badly contaminated material has beenremoved from the recycled material.

SUMMARY OF THE INVENTION

Accordingly, it is a primary object of the present invention to providea method and system for detecting the presence or absence of specificsubstances--e.g., contaminants including but not limited to ammonia,organic nitrogenous compounds and hydrocarbons, in plastic materials.

It is another object of the present invention to provide a system andmethod for detecting specific contaminants in articles made of plasticmaterials, or in shredded, pelletized, or flaked plastic materials, asthe articles or materials move rapidly along a conveyor.

It is another object of the present invention to provide a system andmethod for sampling and analyzing residues in materials as they movealong a conveyor.

It is still another object of the present invention to provide a systemand method for sampling and analyzing residues in materials moving alonga conveyor without contacting the materials being tested with any of thesampling and analyzing mechanisms.

It is yet another object of the present invention to provide a methodfor inspecting used plastic beverage containers for contaminants,shredding the containers into constituent pieces thereof and washing theconstituent pieces in a continuous, in-line process.

The objects of the present invention are fulfilled by providing a methodof sampling and determining the presence of certain volatiles in plasticmaterials to be recycled comprising the steps of: providing a supply ofplastic materials to be recycled; directing fluid (usually a jet of airor CO₂ gas) at said materials in order to displace at least a portion ofvolatiles therein to positions spaced from the materials to form asample cloud at a region spaced from the materials; evacuating a sampleof said portion of the volatiles so displaced by applying suction to thesample cloud at said regions spaced from said materials; and analyzingthe sample evacuated to determine the presence or absence of volatilesof said contaminants in said materials. The procedure may also involveoptical scanning of the plastic for non volatile contaminants. This iscarried out in real time as the bottle or shreds pass by the samplingpoint. Other fluids which may be directed at the materials may includebut are not limited to liquids such as aqueous sodium carbonate (NaCO₃)which enhances liberation of ammonia or amines from the materials.However, NaCO₃ would not be used at an inspection station located aftera washer--i.e., to inspect plastic materials immediately following theirwashing or at any other location further downstream.

In a preferred embodiment the supply of materials is provided from usedbeverage containers of plastic by an in-line shredder or flaker in-linewith the inspection and washing conveyor which shreds or flakes theplastic containers into constituent pieces thereof which are inspectedfor contaminants, sorted and washed.

It is a discovery of the present invention, that the shredding of theplastic containers into pieces, heats the pieces to a temperaturesufficient to vaporize some of the contaminants therein in order to emitvolatiles thereof. Accordingly, it is particularly advantageous toanalyze the emitted volatiles either during or immediately after theshredding of the containers.

It is a further discovery of the present invention that it isparticularly advantageous to test the shredded plastic materials justafter the washing process, again due to the fact that there are hightemperatures associated with the washing process that will liberatevolatiles of contaminants in the plastic material if any are present.

It is still a further discovery of the present invention that it isimportant to maintain the temperature of the washed shredded materialbelow a level that would emit detectable levels of vapors derived fromthe plastic material itself which would create background interferencewith volatiles of any contaminants emitted from the plastic materials.

Further scope of applicability of the present invention will becomeapparent from the detailed description given hereinafter. However, itshould be understood that the detailed description and specificexamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given hereinbelow and the accompanying drawingswhich are given by way of illustration only, and thus, are notlimitative of the present invention and wherein:

FIG. 1 is a schematic block diagram of the sampling and residueanalyzing system of the invention described in U.S. application Ser. No.07/890,863, now U.S. Pat. No. 5,352,611, illustrating a plurality ofcontainers moving seriatim along a conveyor system through a teststation, reject mechanism and washer station; and

FIG. 2 is a schematic block diagram of a system and method forinspecting, shredding, washing and sorting recyclable plastic materialsaccording to the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The system of FIG. 1 is fully disclosed in allowed parent applicationSer. No. 07/890,863, now U.S. Pat. No. 5,352,611, filed Jun. 1, 1992,the entire disclosure of which is incorporated herein by reference.

Referring to FIG. 1 there is illustrated a conveyor 10 moving in thedirection of arrow A having a plurality of uncapped, open-topped spacedcontainers C (e.g. plastic beverage bottles of about 1500 c.c. volume)disposed thereon for movement seriatim through a test station 12, rejectmechanism 28 and conveyor 32 to a washer system. To achieve higher testrates containers C could be touching each other rather than spaced. Thecontents of containers C would typically include air, volatiles ofresidues of contaminants, if any, and volatiles of any products such asbeverages which had been in the containers. An air injector 14 which isa source of compressed air is provided with a nozzle 16 spaced from butaligned with a container C at test station 12. That is nozzle 16 isdisposed outside of the containers and makes no contact therewith.Nozzle 16 directs compressed air into containers C to displace at leasta portion of the contents of the container to thereby emit a samplecloud 18 to a region outside of the container being tested.

As an alternative to compressed air, CO₂ gas could be utilized as theinjected fluid. Also the compressed air or CO₂ gas could be heated toenhance volatility of the compounds being tested.

The column of injected air through nozzle 16 into a container C would betypically of the order of about 10 c.c. to 50 c.c. for bottle speeds ofabout 200 to 1000 bottles per minute. A rate of 400 to 600 bottles perminute is possible and is compatible with current beverage bottlefilling speeds. The desired test rate may vary with the size of thebottles being inspected and filled. Of course the bottles could bestationary or moving slower than 200 bottles per minute and the systemwould still work. Only about 10 c.c. of the container contents would bedisplaced to regions outside of the bottle to form sample cloud 18.

Also provided is an evacuator sampler 22 which may comprise a vacuumpump or the like coupled to a sampling tube or conduit 20. The tube ismounted near, and preferably downstream (e.g., about 1/16 inch) of theair injector 14 so as to be in fluid communication with sample cloud 18adjacent to the opening at the top of containers C.

Neither nozzle 16 nor tube 20 contacts the containers C at test station12; rather both are spaced at positions outside of the containers inclose proximity to the openings thereof. This is advantageous in that nophysical coupling is required to the containers C, or insertion ofprobes into the containers, which would impede their rapid movementalong conveyor 10 and thus slow down the sampling rate. High speedsampling rates of from about 200 to 1000 bottles per minute are possiblewith the system and method of the present invention. The conveyor 10 ispreferably driven continuously to achieve these rates without stoppingor slowing the bottles down at the test station.

A bypass line 24 is provided in communication with the evacuator sampler22 so that a predetermined portion (preferably about 90%) of the samplefrom cloud 18 entering tube 20 can be diverted through bypass line 24.The remaining sample portion passes to a residue analyzer 26, whichdetermines whether undesirable substances are present, and then isexhausted. One purpose of diverting a large portion of the sample fromcloud 18 is to reduce the amount of sample passing from evacuatorsampler 22 to residue analyzer 26 in order to achieve high speedanalysis. This is done in order to provide manageable levels of samplesto be tested by the residue analyzer 26. Another purpose for diverting aportion of the sample is to be able to substantially remove all ofsample cloud 18 by evacuator 22 from the test station area and divertthe excess through bypass line 24. In a preferred embodiment the excessportion of the sample passing through bypass line 24 is returned to airinjector 14 for introduction into the subsequent containers moving alongconveyor 10 through nozzle 16. However, it would also be possible tosimply vent bypass line 24 to the atmosphere.

It should be understood that sample cloud 18 could be analyzed in situwithout transporting it to a remote analyzer such as 26. It could alsobe transported to analyzer 26 by blowing rather than sucking.

A microprocessor controller 34 is provided for controlling the operationof air injector 14, evacuator sampler 22, residue analyzer 26, a rejectmechanism 28 and an optional fan 15. Container sensor 17 includingjuxtaposed radiation source and photodetector is disposed opposite areflector (not shown) across conveyor 10. Sensor 17 tells controller 34when a container arrives at the test station and briefly interrupts thebeam of radiation reflected to the photodetector. Optional fan 15 isprovided to generate an air blast towards sample cloud 18 and preferablyin the direction of movement of containers C to assist in the removal ofsample cloud 18 from the vicinity of test station 12 after eachcontainer C is sampled. This clears out the air from the region of thetest station so that no lingering residues from an existing sample cloud18 can contaminate the test station area when successive containers Creach the test station for sampling. Thus, sample carryover betweencontainers is precluded. The duty cycle for operation of fan 15 iscontrolled by microprocessor 34 as indicated diagrammatically in FIG. 1.Preferably fan 15 is continuously operating for the entire time the restof the system is operating.

A reject mechanism 28 receives a reject signal from microprocessorcontroller 34 when residue analyzer 26 determines that a particularcontainer C is contaminated with a residue of various undesirable types.Reject mechanism 28 diverts contaminated rejected bottles to a conveyor30 and allows passage of uncontaminated, acceptable bottles to a washer(not shown) on a conveyor 32.

An alternative option is to place the bottle test station downstream ofthe bottle washer in the direction of conveyor travel, or to place anadditional test station and sample and residue analyzing system afterthe washer. In fact it may be preferable to position the test stationand system after the washer when inspecting bottles for somecontaminants. For example, if the contaminant is a hydrocarbon, such asgasoline which is insoluble in water, it is easier to detect residues ofhydrocarbons after the bottles have been washed. This is because duringthe washing process in which the bottles are heated and washed withwater, water soluble chemical volatiles are desorbed from the bottles bythe heating thereof and then dissolved in the washing water. Certainhydrocarbons, on the other hand, not being water soluble, may then besampled by a sampler 22 downstream of the washer, to the exclusion ofthe dissolved, water-soluble chemicals. Therefore, the detection of suchhydrocarbons can be performed without potential interference from otherwater soluble chemicals if the bottles pass through a washer beforetesting.

The materials to be inspected are not limited to substances incontainers. For example, the method and system of FIG. 1 could be usedto detect volatiles adsorbed in shredded strips or flakes of thebottles, or plastic stock to be recycled for manufacturing new plasticbeverage bottles or food containers or other articles of plastic. Thisshredded or flaked plastic stock could be placed directly on a conveyorbelt 10 and passed through test station 12 of FIG. 1; or the plasticstock could be placed in baskets, buckets or other types of containersdisposed thereon and inspected in batches.

The system for analyzing volatiles emitted from containers C at teststation 12 in FIG. 1 will be referred to hereinafter with respect toembodiments of the present invention illustrated in FIG. 2 as chemical"sniffing". FIG. 2 illustrates an in-line conveyor system including aconveyor 198 on which a plurality of plastic containers C move through afirst test station 200, and into a shredder or flaker 202. Shreds orflakes F emerging from shredder or flaker 202 pass through a teststation 204, where contaminated flakes are rejected and separated fromcleaner flakes F on their way to a washer 206. The shredded or flakedmaterial F emerging from washer 206 is again inspected at a test station208, and still contaminated flakes of material are rejected.Substantially clean and pure flakes F to be utilized in the fabricationof new plastic containers emerge on conveyor 10 from test station 3.

Each of the test stations 200, 204 and 208 in the system of FIG. 2preferably contains a chemical "sniffer" such as the system disclosed inFIG. 1 at test station 12.

It should be understood that additional test stations could follow teststation 208. For example, there could be a flake pelletizer afterstation 208 and a test station following the pelletizer; an additionaltest station following a preform manufacturing station for new bottlesto test the preforms; and another test station after a blow molder whichblows the preform into new bottles.

There are three different stages of the process illustrated in FIG. 2where chemical sniffing of the plastic flakes F of material can be mosteffective. The first two sampling points at test stations 200 and 204are designed to remove the contaminated material before it goes into thewashing process in washer 206. If the chemical sniffing processes attest stations 200 and 204 are effective, then the effectiveness of thewashing step at washer 206 is less critical. This may allow use of aninexpensive or cost-effective washer 206.

Testing and sampling of the incoming containers C at test station 200 ofFIG. 2 is conducted to find gross contaminants in the containers and tominimize cross-contamination in other steps of pre-processing. Thecontainers C are typically in the form of crushed and/or puncturedbottles at this point, and may be in prone rather than upright position.Monitoring will, for example, find the bottles where liquid has spilledout and has cross contaminated other bottles on their way to theshredder 202. This step is important since a bottle full of engine oil,for example, may contaminate several other bottles if the oil spills.

Containers C which have passed through test station 200, and have notbeen rejected, pass into shredder 202. Heat is generated in the shredder202 as the containers are broken down into pieces. Temperatures of up to200° F. are generated, which can serve to drive off the contaminants sothat they can be more readily detected. An additional advantage ofsampling the shredded material as it emerges from shredder 202 at teststation 204, is that contaminants released from the shredding of asingle contaminated bottle will not have contaminated too much othermaterial. Thus, sampling the fumes from the shredder at test station 204could lead to the rejection from the process stream of flakes ofmaterial F from the bottle in question together with materials from justa few adjacent bottles.

Sampling at the shredder 202, or as close to the newly shredded materialemerging from shredder 202 as possible, is needed so as to avoidcontaminating a large amount of flakes F. That is, any contaminatedflakes emerging from shredder 202 are immediately detected at teststation 204, and rejected in order to avoid contaminating a substantialquantity of flakes on the conveyor 198.

A third test station 208, is designed to detect flakes F as they emergefrom washer 206 in order to monitor the washing process. Again,monitoring is best accomplished where the temperatures are high enoughto assist in the emission of volatiles of contaminants from the flakesof material. Temperatures in the washer are typically from about 190° F.to about 210° F. Monitoring of the post-washed flakes F is for qualityassurance purposes, since the detection of contaminants at this point inthe process will require the automatic rejection of a considerableamount of material due to the mixing of good and bad flakes F in thewashing process.

It is a discovery of the present invention that the temperature of thewash solution used in the washer 206 or in a pelletizer or preform makermust be kept below a temperature at which the plastic material beinginspected will vaporize. Such vaporization would produce detectablebackground volatiles which would tend to interfere with detection ofvolatiles relating to contaminants within the materials. For example,tests were performed on flakes from PET beverage bottles in order todetermine the ability of the analyzing apparatus of the presentinvention to sniff the material without interference from backgroundvolatiles of the PET material itself. Six temperatures were studied, asshown below:

    ______________________________________                                        Temperature °F.                                                                     Observation                                                      ______________________________________                                        80           No background response from PET vapors                           200          No background response from PET vapors                           300          No background response from PET vapors                           400          No background response from PET vapors                           650          No background response from PET vapors                           750          Background response observed                                     ______________________________________                                    

From the above results it was concluded that PET flakes can bechemically sniffed at temperatures of up to about 650° F. without anyeffects from the PET itself on the accurate detection of contaminantswithin the PET flakes.

However, typically the highest temperatures encountered where snifftests would be made would occur at the pelletizing and preform stations,and those temperatures would likely not exceed about 570° F.

Another observation from these experiments is that the washing proceduremust preferably vent the hot vapors from the process stream or riskcontamination of all of the PET material that is in contact withcontaminated vapors in the washer. This is important and differs fromconventional washers since the tendency in prior art systems is to useenclosed systems washers so as to conserve heat and minimize energycost. However, washer 206 has a vent, such as vent 210, to carry hotvapors away from the PET flakes. Shredder 202 may also include a ventfor hot vapors associated with the shredding process.

It should be understood that the present invention may be modified aswould occur to one of ordinary skill in the art without departure fromthe spirit and scope of the present invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

What is claimed is:
 1. A method of determining whether plastic materialobtained from used containers is free of volatiles of contaminants sothat the material can be recycled to produce new containers, comprisingthe steps of:providing a supply of used containers; breaking eachcontainer into pieces of said material, said breaking causing saidpieces to be heated to temperatures sufficient to vaporize thecontaminants and emit volatiles thereof; and testing said volatiles todetermine the presence or absence of said contaminants in saidmaterials.
 2. The method of claim 1 wherein the step of breakingcomprises shredding the plastic material into strips.
 3. The method ofclaim 1 wherein the step of breaking comprises forming flakes of theplastic material.
 4. The method of claim 1 wherein the step of testingcomprises the steps of:directing fluid at said pieces of materials inorder to displace at least a portion of volatiles therein to positionsspaced from the materials to form a sample cloud at a region spaced fromthe materials; evacuating a sample of said portion of the volatiles sodisplaced by applying suction to the sample cloud at said region spacedfrom said materials; and analyzing the sample evacuated to determine thepresence or absence of said contaminants in the materials.
 5. The methodof claim 1 including the additional steps prior to the step of testingof:washing the pieces of plastic material in a heated fluid to remove aportion of contaminants therein, and maintaining the temperature ofwashed material below a level that would emit detectable levels ofvapors derived from the plastic material itself.
 6. The method of claim5 wherein the plastic material is PET and the temperature is maintainedbelow about 650° F.